In recent years, with increased diversification of the image application field, several kinds of displays technology of a large size image plane have been developed.
FIG. 14 is a sectional view illustrating one example of the arrangement of a projector in this kind of technology. Referring to this figure, a liquid crystal light valve 2 in which several pixels are two-dimensionally arrayed is shown. An image signal is inputted to this liquid crystal light valve 2, as is similar to the well-known liquid crystal televisions, and accordingly, the pixels are driven so as to form an image. In this arrangement, the pixels are constituted by, for example, a well-known active-matrix system. A light source 5 for emitting white light to the liquid crystal light valve 2 is located in the rear of the latter. A projection lens 3 focuses light which has passed through the liquid crystal light valve 2 onto a screen 6 for forming an image (this light will hereafter be denoted as "image light").
With the above-mentioned arrangement, when an image signal is supplied to the liquid crystal light valve 2, the pixels are driven in accordance with the image signal so as to form an image in the liquid crystal light valve 2. Further, light passes through this liquid crystal light valve 2 so as to create an intensity-modulated image light. This image light is focused onto the screen 6 by the projection lens 3. As a result, the image formed in the liquid crystal light valve 2 is magnified and projected onto the screen 6, thereby making it possible to display a large size image plane.
The image projected by the projector has a resolution which is determined by the number of pixels that constitute the liquid crystal light valve 2. At present, the number of pixels in the liquid crystal light valve 2 is substantially equal to that of the well-known liquid crystal televisions. Accordingly, the number of pixels per unit area is large in a liquid crystal television having a small size screen, and therefore, it is considered that the liquid crystal light valve 2 can provide an image with a relatively high definition. However, when this image is magnified and projected for displaying a large size image plane, the number of pixels per unit area decreases, and accordingly, the pixel density is lowered, resulting in an image having a low resolution.
Accordingly, at present, the objective is to increase the pixel density or the size of a liquid crystal panel itself. Thus, a liquid crystal light valve 2 displaying on a high definition television (HDTV) have been being developed. However, in the case where increasing the density of pixels in the liquid crystal light valve 2, the production yield is greatly reduced in the present manufacturing process, resulting in a high manufacturing cost. Further, there is a technical limitation in that the length of one side of one pixel cannot be less than the thickness of a liquid crystal panel even though the size of one pixel is reduced in order to increase the pixel density. Further, in the case where increasing the size of the liquid crystal panel itself so as to increase the number of pixels, the production yield decreases, similar to the situation resulting when of increasing the pixel density is increased, causing a high cost. That is, an increase, exceeding the present available number, in the number of pixels in the liquid crystal light valve 2 is very difficult to achieve, and accordingly, it has been difficult to increase the definition of a magnified image.
Accordingly, in order to avoid incurring the abovementioned problems caused by an increase in the number or the density of pixels in the liquid crystal light valve 2, a projector which can effectively increase the definition of the projected image has been proposed, without increasing the number of pixels in the liquid crystal light valve 2. FIG. 15 is a schematic view illustrating one example of this arrangement. In this figure, like reference numerals are attached to like parts to those shown in FIG. 14, and an explanation thereto is omitted.
In the projector shown in this figure, a prism mirror PM having two reflecting surfaces is located in the rear of the projecting lens 3. This prism mirror PM bisplits the optical axis m so as to form two image planes. Further, two liquid crystal light valves 21, 22 and two light sources 51, 52 for emitting light to the former are arranged corresponding to these two image planes. With this arrangement, images displayed on these two liquid crystal light valves 21, 22 are projected by means of the lens 3 onto the right and left halves of the screen 6, respectively, so that a continuous projected image can be obtained on the screen 6. That is, as shown in FIG. 15, the image given by the liquid crystal light valve 22 is displayed over the area indicated by A on the screen 6 while the image given by the liquid crystal light valve 21 is displayed over the area indicated by B on the screen. Accordingly, an image signal to be fed to these two liquid crystal light valves 21, 22 is divided into two for the respective areas, and are then inputted to the liquid crystal light valves 21, 22 so as to display the original image on the screen. In this arrangement, in which the display images in the two liquid crystal light valves are synthesized so as to display the original image, it is possible to obtain a pixel density which is two times as great as that conventionally obtained.
However, with this type of projector, the following disadvantages have been inevitably arisen. That is, if the characteristics of the liquid crystal light valves 21, 22 for forming left and right projected images are different, a joint seam becomes visible on the screen, being caused by a difference between the characteristics thereof, and accordingly, the quality of the projected image deteriorates. Further, in the above-mentioned projector, since the effective display areas of the liquid crystal light valves are increased, the size of the projection lens has to be increased.